diff --git a/packages/studio/src/captions/store.ts b/packages/studio/src/captions/store.ts
new file mode 100644
index 0000000000..48f9b1ca37
--- /dev/null
+++ b/packages/studio/src/captions/store.ts
@@ -0,0 +1,270 @@
+import { create } from "zustand";
+import {
+  CaptionAnimation,
+  CaptionAnimationSet,
+  CaptionContainerStyle,
+  CaptionModel,
+  CaptionStyle,
+} from "./types";
+
+interface CaptionState {
+  isEditMode: boolean;
+  model: CaptionModel | null;
+  selectedSegmentIds: Set<string>;
+  selectedGroupId: string | null;
+  sourceFilePath: string | null;
+
+  // Basic
+  setEditMode: (active: boolean) => void;
+  setModel: (model: CaptionModel | null) => void;
+  setSourceFilePath: (path: string | null) => void;
+
+  // Selection
+  selectSegment: (id: string, additive?: boolean) => void;
+  selectGroup: (id: string) => void;
+  selectAll: () => void;
+  clearSelection: () => void;
+
+  // Segment mutations
+  updateSegmentStyle: (segmentId: string, style: Partial<CaptionStyle>) => void;
+  updateSegmentText: (segmentId: string, text: string) => void;
+  updateSegmentTiming: (segmentId: string, start: number, end: number) => void;
+
+  // Group mutations
+  updateGroupStyle: (groupId: string, style: Partial<CaptionStyle>) => void;
+  updateGroupContainer: (groupId: string, container: Partial<CaptionContainerStyle>) => void;
+  updateGroupAnimation: (
+    groupId: string,
+    phase: keyof CaptionAnimationSet,
+    animation: Partial<CaptionAnimation>,
+  ) => void;
+  splitGroup: (groupId: string, atSegmentId: string) => void;
+  mergeGroups: (groupId1: string, groupId2: string) => void;
+
+  // Bulk
+  updateSelectedStyle: (style: Partial<CaptionStyle>) => void;
+  applyAnimationToAll: (animation: CaptionAnimationSet) => void;
+
+  // Reset
+  reset: () => void;
+}
+
+const initialState = {
+  isEditMode: false,
+  model: null,
+  selectedSegmentIds: new Set<string>(),
+  selectedGroupId: null,
+  sourceFilePath: null,
+};
+
+export const useCaptionStore = create<CaptionState>((set, get) => ({
+  ...initialState,
+
+  // Basic
+  setEditMode: (active) => set({ isEditMode: active }),
+  setModel: (model) => set({ model }),
+  setSourceFilePath: (path) => set({ sourceFilePath: path }),
+
+  // Selection
+  selectSegment: (id, additive = false) =>
+    set((state) => {
+      if (additive) {
+        const next = new Set(state.selectedSegmentIds);
+        if (next.has(id)) {
+          next.delete(id);
+        } else {
+          next.add(id);
+        }
+        return { selectedSegmentIds: next, selectedGroupId: null };
+      }
+      return { selectedSegmentIds: new Set([id]), selectedGroupId: null };
+    }),
+
+  selectGroup: (id) =>
+    set((state) => {
+      const group = state.model?.groups.get(id);
+      if (!group) return {};
+      return {
+        selectedSegmentIds: new Set(group.segmentIds),
+        selectedGroupId: id,
+      };
+    }),
+
+  selectAll: () =>
+    set((state) => {
+      if (!state.model) return {};
+      return {
+        selectedSegmentIds: new Set(state.model.segments.keys()),
+        selectedGroupId: null,
+      };
+    }),
+
+  clearSelection: () => set({ selectedSegmentIds: new Set(), selectedGroupId: null }),
+
+  // Segment mutations
+  updateSegmentStyle: (segmentId, style) =>
+    set((state) => {
+      if (!state.model) return {};
+      const segment = state.model.segments.get(segmentId);
+      if (!segment) return {};
+      const segments = new Map(state.model.segments);
+      segments.set(segmentId, { ...segment, style: { ...segment.style, ...style } });
+      return { model: { ...state.model, segments } };
+    }),
+
+  updateSegmentText: (segmentId, text) =>
+    set((state) => {
+      if (!state.model) return {};
+      const segment = state.model.segments.get(segmentId);
+      if (!segment) return {};
+      const segments = new Map(state.model.segments);
+      segments.set(segmentId, { ...segment, text });
+      return { model: { ...state.model, segments } };
+    }),
+
+  updateSegmentTiming: (segmentId, start, end) =>
+    set((state) => {
+      if (!state.model) return {};
+      const segment = state.model.segments.get(segmentId);
+      if (!segment) return {};
+      const segments = new Map(state.model.segments);
+      segments.set(segmentId, { ...segment, start, end });
+      return { model: { ...state.model, segments } };
+    }),
+
+  // Group mutations
+  updateGroupStyle: (groupId, style) =>
+    set((state) => {
+      if (!state.model) return {};
+      const group = state.model.groups.get(groupId);
+      if (!group) return {};
+      const groups = new Map(state.model.groups);
+      groups.set(groupId, { ...group, style: { ...group.style, ...style } });
+      return { model: { ...state.model, groups } };
+    }),
+
+  updateGroupContainer: (groupId, container) =>
+    set((state) => {
+      if (!state.model) return {};
+      const group = state.model.groups.get(groupId);
+      if (!group) return {};
+      const groups = new Map(state.model.groups);
+      groups.set(groupId, {
+        ...group,
+        containerStyle: { ...group.containerStyle, ...container },
+      });
+      return { model: { ...state.model, groups } };
+    }),
+
+  updateGroupAnimation: (groupId, phase, animation) =>
+    set((state) => {
+      if (!state.model) return {};
+      const group = state.model.groups.get(groupId);
+      if (!group) return {};
+      const groups = new Map(state.model.groups);
+      const existingPhase = group.animation[phase];
+      const mergedPhase =
+        existingPhase !== null
+          ? { ...existingPhase, ...animation }
+          : (animation as CaptionAnimation);
+      groups.set(groupId, {
+        ...group,
+        animation: { ...group.animation, [phase]: mergedPhase },
+      });
+      return { model: { ...state.model, groups } };
+    }),
+
+  splitGroup: (groupId, atSegmentId) =>
+    set((state) => {
+      if (!state.model) return {};
+      const group = state.model.groups.get(groupId);
+      if (!group) return {};
+
+      const splitIndex = group.segmentIds.indexOf(atSegmentId);
+      if (splitIndex <= 0) return {};
+
+      const firstIds = group.segmentIds.slice(0, splitIndex);
+      const secondIds = group.segmentIds.slice(splitIndex);
+
+      const newGroupId = `group-${Date.now()}-${Math.random().toString(36).slice(2)}`;
+      const groups = new Map(state.model.groups);
+      groups.set(groupId, { ...group, segmentIds: firstIds });
+      groups.set(newGroupId, { ...group, id: newGroupId, segmentIds: secondIds });
+
+      const orderIndex = state.model.groupOrder.indexOf(groupId);
+      const groupOrder = [...state.model.groupOrder];
+      groupOrder.splice(orderIndex + 1, 0, newGroupId);
+
+      // Update groupIndex for segments in the new second group
+      const segments = new Map(state.model.segments);
+      secondIds.forEach((segId, idx) => {
+        const seg = segments.get(segId);
+        if (seg) {
+          segments.set(segId, { ...seg, groupIndex: idx });
+        }
+      });
+
+      return { model: { ...state.model, groups, segments, groupOrder } };
+    }),
+
+  mergeGroups: (groupId1, groupId2) =>
+    set((state) => {
+      if (!state.model) return {};
+      const group1 = state.model.groups.get(groupId1);
+      const group2 = state.model.groups.get(groupId2);
+      if (!group1 || !group2) return {};
+
+      const mergedSegmentIds = [...group1.segmentIds, ...group2.segmentIds];
+
+      const groups = new Map(state.model.groups);
+      groups.set(groupId1, { ...group1, segmentIds: mergedSegmentIds });
+      groups.delete(groupId2);
+
+      const groupOrder = state.model.groupOrder.filter((id) => id !== groupId2);
+
+      // Update groupIndex for segments from group2
+      const segments = new Map(state.model.segments);
+      group2.segmentIds.forEach((segId, idx) => {
+        const seg = segments.get(segId);
+        if (seg) {
+          segments.set(segId, { ...seg, groupIndex: group1.segmentIds.length + idx });
+        }
+      });
+
+      // Clear selection if it referenced group2
+      const selectedGroupId = get().selectedGroupId === groupId2 ? null : get().selectedGroupId;
+
+      return { model: { ...state.model, groups, segments, groupOrder }, selectedGroupId };
+    }),
+
+  // Bulk
+  updateSelectedStyle: (style) =>
+    set((state) => {
+      if (!state.model || state.selectedSegmentIds.size === 0) return {};
+      const segments = new Map(state.model.segments);
+      for (const segmentId of state.selectedSegmentIds) {
+        const segment = segments.get(segmentId);
+        if (segment) {
+          segments.set(segmentId, { ...segment, style: { ...segment.style, ...style } });
+        }
+      }
+      return { model: { ...state.model, segments } };
+    }),
+
+  applyAnimationToAll: (animation) =>
+    set((state) => {
+      if (!state.model) return {};
+      const groups = new Map(state.model.groups);
+      for (const [id, group] of groups) {
+        groups.set(id, { ...group, animation });
+      }
+      return { model: { ...state.model, groups } };
+    }),
+
+  // Reset
+  reset: () =>
+    set({
+      ...initialState,
+      selectedSegmentIds: new Set<string>(),
+    }),
+}));